Scaling up?


The online magazine Next City quotes me in an informative story about urban farming.

Dunn admits there aren't enough high-end restaurants or CSA customers willing to pay a premium for the produce generated by 10 or 20 one-acre [urban] farms, much less 10,000. He's looking for alternative buyers, such as hospitals or schools, but has yet to hit on a scalable option.

So-called "vertical farms" have additional problems, but I run into this scaling problem all the time.

When I was at UC Davis, people gushed about how much "more sustainable" a farm that grew seeds of native plants was, relative to those growing wheat, almonds, or tomatoes. Great, but that one farm pretty much saturated the market for native-plant seeds.

My brother earns a reasonable income growing wonderful vegetables and fruits organically, but that doesn't mean it would be easy to convert all our farms to organic methods. If each acre of organic farm needs manure from chickens fed corn from four acres of land fertilized with synthetic fertilizer, that seems to set an upper limit of 25% for organic farmland. Long before that, though, we might run out of customers willing to pay organic premium prices.


Have to complain about your math...
IF (and I can complain about the assumptions too, but...) If each acre of organic farm needs four acres of "support" land to generate the feed for enough chickens... then the upper limit for organic acres is 20% (4:1 - BUT that is 1 acre in 5).

Back to the assumption - you're assuming the chicken feed can only be from synthetically fertilized corn. But part of a chicken diet can be soy. Soy is more easily grown organically (no N fertilizer requirement) This actually helps get you back to an upper bound of 25%, but could go further.

What happens if we harvest seaweed for composting for organic fertilizer? What if we feed organic plant debris not used for human food (husks, stalks) to ruminants and then use their manure? My only point here is that trying to set an upper limit on the number of potential organic acres is pretty tough. And tougher still if we don't account for our acres appropriately.

Right again, Clem, at least about my math. I got it right on p. 105 of my book.

I agree that nitrogen-fixing soybeans could be fed to chickens as a source of manure not ultimately dependent on nitrogen fertilizer. But soybeans have lower yield than corn, so it would take even more acres to feed enough chickens to get a given amount of manure. How much of US soybean production is organic?

I bet it would take at least ten times as much energy to transport seaweed and seaweed compost as it does to make nitrogen fertilizer, except for farms right on the coast -- another case where something that might work on a small scale can't be scaled up. See the top of p. 15.

Where does the N and P in the crop residues come from?

Not all yield is the same... even the bushels don't match. In the US for trade purposes a bushel of corn is 56lb and a bushel of soy is 60lb. But you do still get far more pounds of corn per acre than soy. So what else does soy have going for it? On a dry matter basis a soybean seed is roughly 40% protein and 20% oil. A corn kernel on the other hand is roughly 75% starch, 9% protein, and 4% oil. So we're not comparing apples to apples :) And for these same reasons you wouldn't completely switch soy for corn in the chicken diet.

You can genetically modify the degree of starch/protein/oil in the seed of both species, but not to the extent you could breed a corn hybrid that would make 40% protein and 20% oil. Further, as we breed these crops for bushels per acre alone (not accounting for seed constituents) the typical result is more CHO and less protein and oil (even in soy).

I don't have exact numbers, but will suggest that the US organic soy crop is safely less than 10% and likely even less than 4% of all soy acres.

Agreed - seaweed only makes sense on the coast. Algal biomass could make some sense in the interior on marginal lands or next to coal fired power plants as a CO2 sink. Neither is a complete fix; but neither should be wholly dismissed for not being a complete solution.

In organic systems that I'm aware of you can use rock phosphate for P fertilizing. Not that it does a whole lot of good in the short term (as far as making P available) but it can help some. Also - cover crops can help mobilize P (and leguminous covers can fix N). And both legumes and rock phosphate together won't come close to providing the N and P needed as fertilizer for the crops we need to produce to feed ourselves in the manner we are currently.

So I'm basically agreeing with you in broad stripes. But details...

Ford, I really liked your book even though I’m what you call a ‘self-styled agroecologist’ or ‘misguided mimicry’ type (I wrote a review of it which will be coming out in Permaculture Magazine, if you’re interested). But I think you tend to make quite conventional assumptions about the present and likely future socioeconomic context within which farming takes place. Why are CSA vegetables so costly? Well here in the UK it’s because growers don’t get the same level of subsidies that broadscale farmers do, their land is costlier, their product is labour intensive rather than energy intensive, and they’re undercut by mostly foreign competitors who use poorly paid labour and who are sucking the water out of their arid landscapes. I imagine it’s a similar picture in the US. So yes there may not be enough customers willing to pay a premium for their local CSA produce, but maybe that’s because people have got too used to not paying for the true costs of their food – and maybe that will have to change.

On the organic scale up point, I reckon I can grow crops reasonably sustainably on about 70% of my holding if I grow leguminous cover crops on the other 30% without importing anything much, although I suppose P ultimately may be a problem, but then the same goes for conventional farmers? Anyway, that’s a different slant to your 25% figure – I don’t think organic farming should always just be equated with importing non-organic manure. But until somebody’s figured out how to produce endless clean energy, maybe we should be husbanding our synthetic fertiliser a bit better – use it where it’s really needed (ie. probably not much in the US or the UK), switch to organic wherever we can and eat less meat?


Sorry about the delay in posting your comment, which my software mistook for spam. I have no idea why.

I agree with most of what you wrote -- or at least don't disagree, in cases where I have less information. Can you explain your estimate of 30% as the land area of legumes that could meet the N needs of the other 70%? That seems optimistic, at least for current practices and available cultivars. I suspect, however, that an evolutionary perspective on symbiosis could lead to substantial improvements in biological nitrogen fixation. That's the main focus of my own research.

I agree with your comments on phosphorus and don't have a good solution to this problem.


I'm wondering if you'd mind following up on your assertion that land for growers is costlier than land for broadscale farmers? Is there actually some sort of government manipulation of farmland value depending upon its use? Are taxes more onerous? Where is the higher land cost coming from?

You're point about subsidies for broadscale ag vs veges won't be contested by me. Here in the States the situation may be comparable, but change might be in the air. While I haven't anything concrete to point at my sense is this latter issue will begin to receive more attention. Here's hoping.

And thanks for stopping by. Followed the link to your blog and see that I'll need to have a closer look at what you're up to.


Thanks for replying to my post. On the land cost side of things, over here it's largely location and scale driven. CSA type growers are mostly looking for peri-urban land close to population centres, and land prices are higher because of pressure for alternative non-agricultural uses. Also the smaller parcels of land sought by horticultural growers tend to have a higher per acre price than larger parcels - not least because wealthy urban horse owners are often willing to pay huge prices for small paddocks. Ten years ago average agricultural land in the UK was going for about £3000 per acre, whereas now it's about £8000, and I've seen one acre horse paddocks go for about £25000. I don't think it's because agriculture is more buoyant, but because people are buying land speculatively or for inheritance tax/subsidy reasons more or less divorced from actual agricultural production - maybe it's the old Mark Twain adage about buying land cos they ain't making it any more, which probably applies even more on our overcrowded little island than the US. Unfortunately we're not properly protecting our agricultural land here and we rely on importing most of our fruit and veg - a high risk strategy in my opinion.

On the 70/30 figure, maybe it is optimistic - I'm referring to a horticultural rotation with a 2 year ley and a 5 year potato and veg rotation including legumes undersown to the crops, as popularised by Iain Tolhurst ('Growing Green'). Other inputs to our overall system include our compost toilet, some livestock scratching around the margins, and some hedge trimmings and such like. I can't claim to have fully implemented it and properly measured outputs against endogenous resource inputs (which is something I'd like to do) - I daresay there's some soil mining going on and obviously lower overall macronutrient productivity than pure cereal production. I guess my main point is that there may be a variety of ways of cycling nutrients endogenously in organic systems, so that organic farming/growing isn't reducible to simply importing manure from off site as people often suppose (especially non-organic manure, which is a restricted practice under organic standards).

I'm trying to research my system, but it's a bit tricky with limited resources and lacking a proper scientific background in this. I'm establishing a little trial this year that I've described here: . I'd welcome your comments on it if you have a chance to look at it.

Not sure when my review of your book is coming out - I'm planning to post it on my blog within the next couple of weeks, so I'll let you know. Thanks for your writing and making your work accessible to growers like me - much food for thought...


I like your experiment, in principle. The Tolhurst system seems like it could be self-sufficient for nitrogen. One thing to keep in mind is that soil organic N reserves can last for years, so early results may not predict long-term ones. That also suggests making the experiment as simple as possible, to increase your chance of continuing long enough to get results.


Hi Chris:
Thanks for the land price explanation. Your experience is not all that different from what I see here in Ohio. The closer to an urban area the more a parcel will bring when sold. Horses figure in the issue here as well. Those who have the means to buy land without the need to earn a return on it can increase the difficulty for the rest.

I clicked through to your blog and had a cursory look at your explanation for your current land issue with what looks to me to be a zoning council of some sort. You are currently waiting on a decision from an appeal by three or more in a situation akin to your own (or you are one of the three?)? Am I understanding correctly - you are trying for a temporary shelter (5 years)? The prospect of a permanent dwelling is off the table?

If I can manage to keep up through your blog I will - am fairly interested as I recently purchased a small(ish) piece of ground. Have had the trespass issue, and wildlife poaching, so my level of sympathy is pretty high. Our zoning laws don't seem anywhere near as onerous as what I perceive yours to be.

Best of luck.

Thanks for your comments again.

Yes I think the zoning laws here are more restrictive - basically if you buy agricultural land you have to show you have an 'essential need' to live on it, which would be fair enough except that many farmhouses and farm buildings have been sold off as separate residential units, and the criteria for 'essential need' are so restrictive that it creates huge obstacles for anyone who isn't either born into farming or independently wealthy. You end up spending years fighting legal battles rather than actually farming.

My recent blog post wasn't about my own application for a dwelling(see for a take on that) but about a similar application for 3 smallholdings not so far away from me here in southwest England under the auspices of the Ecological Land Coop In these times of austerity their council is spending £40,000 trying to prevent them from starting up their business, despite their own officers recommending approval. I like to think that small 'ecological' farmers like us can at the very least deliver on the 'bet hedging' strategy that Ford discusses in his book, but rural policy here is such that we have to fight for the right to exist.

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